<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>底层原理</title>
</head>

<body>
    <div id="app"></div>

    <script>
        var data = {
            a: 10
        };
        document.getElementById("app").innerHTML = data.a;
        Object.defineProperty(data, "a", {
            set(value) {
                document.getElementById("app").innerHTML = value;
            }
        });

    </script>
</body>

</html>